The objective of this proposed study is to obtain measurements of pressure pulse, velocity profile, and wall shear stresses at various sites in the coronary circulation of large horses. Coronary arteries in horses may reach 1 cm. or more in diameter. This species is thus proposed for study because vessels are large enough to permit measuring these flow properties with greater resolution, at bifurcations, and at smaller tributaries. These measurements will be analyzed with particular emphasis on the effects of geometry, Reynolds number, and the unsteadiness parameter. Included will be a study of the influence of aortic flow disturbances on the nature of coronary flow. Pressures will be recorded with cathter-tip manometers, and velocity and wall shear stresses will be measured by hot-film anemometry. These studies in horses, in addition to permitting measurement with increased resolution, are designed to extend the range of measurements in vivo, to animals larger than man. They are believed to have significance to the understanding of the hemodynamic factors in arterial disease.